1. Field of the Invention
The present invention relates to a surface inspection apparatus that inspects foreign substances, flaws, and other defects present on surfaces of objects such as semiconductor wafers or ceramic substrates.
2. Description of the Related Art
If foreign substances, flaws, or other defects are present on the surface of a semiconductor wafer, semiconductor devices fabricated using such semiconductor wafer will be defective. Accordingly, the wafer needs inspection by a surface inspection apparatus to scan for defects. The surface inspection apparatus irradiates the wafer surface with laser light, receives the light reflected from the wafer, and compares the light signal with a threshold value to determine whether the wafer is nondefective. At this time, the wafer is fixed by a substrate-holding jig and rotated at a predetermined speed by a spindle. Simultaneously with the rotation by the spindle, the wafer is moved rectilinearly by a stage. The rotation by the spindle and the linear movement by the stage make the laser light helically scan the wafer surface in relative form. The entire wafer surface is inspected during the scan. In manufacturing lines, the inspection apparatus may also be used with a view to monitoring an occurrence status of dust raised from manufacturing apparatuses.
With the miniaturization of semiconductor circuit width in recent years, the foreign substances, flaws, and other surface defects becoming a problem if they stick to wafers are also being miniaturized in size. The dimensional miniaturization of these defects is, in turn, increasing the number of defects likely to become a problem, and this tendency is bringing about a call for further improvement of the internal cleanliness of apparatuses.
Among existing techniques relating to the cleaning of an inspection apparatus are those described primarily in JP-2011-75351-A, JP-2010-236948-A, and JP-1995-230037-A. JP-2011-75351-A discloses a technique in which multiple fan-filtering units, each of which comprises a fan and exhaust unit for supplying clean air, are disposed and flow rates of air in each of the fans and exhaust units are controlled to suppress a disturbance in the apparatus internal air flow and reduce the volume of foreign matter likely to stick to a wafer.
JP-2010-236948-A discloses suppressing a disturbance in an air flow near a semiconductor wafer by incorporating louver and exhaust unit structural design considerations for reduced sticking of foreign matter to the wafer.
JP-1995-230037-A discloses adopting a downward flow scheme and exhaust unit structure for reduced sticking of foreign matter to a wafer.
Other related techniques include those proposed in JP-2000-230910-A, U.S. Pat. No. 7,420,668, U.S. Pat. No. 7,372,559, and U.S. Pat. No. 6,005,660.